The present invention provides for methods for transferring devices from one substrate to another substrate. More specifically, embodiments of the present invention relate to methods for transferring devices, particularly optoelectronic devices, from carrier substrates to device substrates.
When making a typical optoelectronic apparatus according to one conventional method, a number of individual photodetectors can be formed on a gallium arsenide (GaAs) substrate. After they are formed, the photodetectors may be removed from the GaAs substrate and separated from each other. Each individual photodetector is manipulated, aligned with a device region on a device substrate, and then bonded to the device region. Additional photodetectors are bonded to other device regions on the device substrate in a similar manner and a device assembly is formed. The device assembly can be joined to other assemblies of the same or different type to form an optoelectronic apparatus.
While methods such as this one can be effective in some instances, such methods could be improved. For example, separately manipulating, aligning, and bonding each device to a device substrate is time consuming and labor intensive. The added time and labor needed to form the desired assembly can increase the cost of the assembly. Moreover, alignment errors can occur during the alignment of each device. As the number of device alignment steps increase, the probability that at least one device is misaligned in the desired assembly increases and the likelihood that the desired assembly may be inoperable also increases. Rework of the formed assembly may be needed. Reworking the assembly can increase the cost of the resulting assembly.
Therefore, what is needed and what has been invented is a device transfer method which overcomes the foregoing problems. What is further needed and what has been invented is a device transfer method wherein devices which are to be transferred are placed in controlled directions including tilted and vertical directions.
Embodiments of the invention are directed to methods for efficiently placing devices on device substrates. Advantageously, in some embodiments of the invention, different device pluralities in a device array can be placed on different device substrates using as few as one alignment step and one device bonding step per device substrate. The number of alignment and bonding steps can be reduced in comparison to conventional methods, and the cost of producing the device assemblies and apparatuses can also be reduced. Accordingly, embodiments of the invention are particularly well suited for mass manufacturing device assemblies.
An embodiment of the invention is directed to a method of forming a device assembly. The method includes: forming a first and second plurality of devices on a formation substrate; transferring the first plurality and the second plurality of devices to a carrier substrate; placing the first plurality of devices on a first plurality of device regions on the first device substrate; and placing the second plurality of devices on a second plurality of device regions on a second device substrate.
Another embodiment of the invention is directed to a method for placing device pluralities on multiple device substrates. The method comprises: providing an array of devices on a carrier substrate, wherein the array comprises multiple device pluralities having devices in predetermined patterns; and respectively placing the device pluralities on device regions in predetermined patterns corresponding to the predetermined patterns of the device pluralities. Preferably, the predetermined patterns of device regions are present on respectively different device substrates.
Further embodiments of the invention include a method for transferring a device from one substrate to another substrate comprising coupling a device to a generally horizontal surface of a first substrate; tilting the device with respect to the generally horizontal surface of the first substrate; and transferring the tilted device from the first substrate to a second substrate. Coupling comprises disposing a release layer on the generally horizontal surface of the first substrate; disposing at least one tilting layer on the release layer; and placing the device on the tilting layer. Tilting of the device comprises releasing at least a portion of the release layer from the horizontal surface of the first substrate. The device may be selected from the group consisting of filters, tunable filters, light modulators, optical switches, light-emitting devices, photodetectors, capacitors, resistors, inductors, integrated circuits, and LSIs.
Another embodiment of the present invention provides a method comprising: forming a first and second plurality of devices on a formation substrate; transferring the first plurality and the second plurality of devices to a carrier substrate; tilting the first plurality and the second plurality of devices with respect to a horizontal surface of the carrier substrate; placing the first plurality of devices on a first plurality of device regions on a first device substrate; and placing the second plurality of devices on a second plurality of device regions on a second device substrate. The method further comprises bonding the first plurality of devices to the first plurality of device regions; and bonding the second plurality of devices to the second plurality of device regions. The method may also comprise bonding the first plurality of devices to the first plurality of device regions using a bonding material disposed on the first plurality of device regions; and bonding the second plurality of devices to the second plurality of device regions using a bonding material disposed on the second plurality of device regions. After forming the first and second plurality of devices on the formation substrate, trenches may be formed to separate each of the devices in the first and second plurality from each other. The first and second pluralities of devices may have the same pattern. At least one device in the first device plurality on the carrier substrate may be disposed between at least two adjacent devices in the second device plurality. The first and second plurality of devices may be separated from the formation substrate using a lift-off process. More specifically, prior to transferring, the first and second plurality of devices may be separated from the formation substrate using an epitaxial liftoff process. The first and second pluralities of devices may be formed on a release layer disposed on the formation substrate. The first plurality of devices comprises at least one of a wavelength filter, a mirror, a hologram, a grating, a light-emitting film, a photodiode, a VCSEL, an optical switch, a photonic crystal, an LD, a photo detector, a transceiver chip, an IC, an LSI, a light modulator, a tunable filter, a wavelength switch and a thin film structure. A capacitor-embedded film may be formed using the first plurality of devices on the first device substrate.
The method further comprises providing a third plurality of devices and a fourth plurality of devices on a second carrier substrate; tilting the third plurality and fourth plurality of devices with respect to a horizontal surface of the second carrier substrate; placing the third plurality of devices on a third plurality of device regions on the first device substrate; and placing the fourth plurality of devices on a fourth plurality of device regions on the second device substrate, wherein the devices in the first plurality of devices and the devices in the third plurality of devices have different operational characteristics. The method may also further comprise providing a third plurality of devices, a fourth plurality of devices, and open regions on a second carrier substrate; tilting the third plurality and fourth plurality of devices with respect to a horizontal surface of the second carrier substrate; placing the third plurality of tilted devices on a third plurality of device regions on the first device substrate so that devices already on the first device substrate are disposed in the open regions; and placing the fourth plurality of tilted devices on a fourth plurality of device regions on the second device substrate so that devices already on the second device substrate are disposed in the open regions.
The method may alternatively further comprise bonding the first plurality of tilted devices to the first plurality of device regions using a first bonding material; and bonding the second plurality of devices to the second plurality of device regions using a second bonding material, wherein the first and second bonding materials include at least one of a diffusion bondable metal and solder. The method may also alternatively include bonding the first and second tilted device pluralities to the device regions on the first and second device substrate using a first bonding material; providing a third plurality of devices and a fourth plurality of devices on a second carrier substrate; tilting the third plurality and fourth plurality of devices with respect to a horizontal surface of the second carrier substrate; bonding the third plurality of tilted devices to a third plurality of device regions on the first device substrate using a second bonding material; and bonding the fourth plurality of tilted devices to a fourth plurality of device regions on the second device substrate using the second bonding material, wherein the first bonding material has a higher bonding temperature than the second bonding material. The first and second device pluralities may comprise optoelectronic devices, and the formation substrate may be crystalline.
The first and second device pluralities may be disposed in a device array wherein the device array comprises at least two groups of devices, and each device group comprises at least one device from the first plurality of devices and at least one device from the second plurality of devices. The first device plurality may be aligned with the first plurality of device regions; and the second device plurality may be aligned with the second plurality of device regions, wherein aligning the second device plurality with the second plurality of device regions comprises shifting the carrier substrate a distance approximately equal to a dimension of a device in the array. Each device group may include a dimension of about Px and about Py, and at least two adjacent device regions on the first device substrate may be separated by a distance approximately equal to about Px or about Py. Placing the first plurality of devices on the first plurality of device regions comprises simultaneously placing the devices in the first plurality of devices on the first plurality of device regions; and placing the second plurality of devices on the second plurality of device regions comprises simultaneously placing the devices in the second plurality of devices on the second plurality of device regions. The device regions on the first device substrate correspond to the locations of input and output terminals of a chip to be mounted to the first device substrate, and wherein the first and second plurality of devices comprises at least one of a photodetector, a photodetector amplifier, a VCSEL, and a VCSEL driver. A chip may be bonded to the first device substrate. The first plurality of device regions and the second plurality of device regions may be at locations corresponding to input and output terminals of the chip, and at least some devices in the first plurality of devices may not be disposed directly under an input or an output terminal of the chip disposed on the device assembly. The method may further comprise, after placing the first and second device pluralities on the first and second device substrates, disposing a cover layer over the first and second device pluralities to embed the first and second device pluralities to form first and second device assemblies. A first plurality of waveguides may be formed on the first device substrate and a second plurality of waveguides may be formed on the second device substrate, such that the waveguides communicate with the devices in the first and second device pluralities. A polymeric cover layer may be deposited on the first device substrate over the first device plurality; and the cover layer may be planarized. The first device substrate may subsequently be removed from the first device plurality.
A further embodiment of the invention provides a method for forming an apparatus comprising forming a first device assembly (e.g., a polymer smart pixel) by using any of the methods of the invention; forming a second device assembly (e.g., a multichip module or a chip scale package or an interface chip layer) by forming an apparatus comprising the first and second device assemblies. Forming the apparatus further comprises laminating the first and second device assemblies to each other.
Embodiments of the present invention are directed to a method for placing device pluralities on device substrates comprising providing an array of devices on a carrier substrate having a generally horizontal surface, wherein the array comprises multiple device pluralities having devices in predetermined patterns; tilting the device pluralities with respect to the generally horizontal surface of the carrier substrate; and respectively placing the tilted device pluralities on device substrates having device regions in predetermined patterns corresponding to the predetermined patterns of the device pluralities. The tilted device pluralities may be bonded to device regions on each of the device substrates using a bonding material. The tilted device pluralities may be respectively aligned with the device regions on the respective device substrates. Each respective alignment preferably comprises shifting the carrier substrate a distance approximately equal to Nxc3x97d, wherein d is approximately equal to a dimension of a device in the array or a pitch of the devices in the array, and wherein N is an integer of at least one. The array of devices may include groups of devices, wherein each group includes at least one device from each of the tilted device pluralities. The array may alternatively comprise multiple device groups, with each device group including dimensions of about Px and about Py, and wherein adjacent device regions on the device substrates are separated by a distance of about Px or about Py. The array of devices may include groups of devices, and each group may include at least one device from each of the tilted device pluralities; and the device groups may have a pitch in the array, wherein the device group pitch is equal to the pitch of the device regions of each of the device substrates.
Another further embodiment of the present invention provides a method for placing device pluralities on device substrates comprising providing an array of devices on a carrier substrate having a generally horizontal surface, wherein the array comprises multiple device pluralities having devices in predetermined patterns; tilting the device pluralities with respect to the generally horizontal surface of the carrier substrate; and respectively placing the device pluralities on predetermined patterns of device regions corresponding to the predetermined patterns of the device pluralities. The predetermined patterns of device regions may be respectively disposed on different or the same device substrates. The method further comprises mounting a chip on the first device substrate, wherein the device regions on the first device substrate correspond to the locations of input and output terminals of the chip mounted on the first device substrate. The second device assembly may be formed on the first device assembly using a build-up process.
These and other embodiments will be described in more detail below.